As an example of an environment recognition apparatus comprising a three-dimensional vision sensor in the active sensor type, a technique mentioned in Patent Document Reference 1 can be cited. The apparatus mentioned in Reference 1 is mounted on an autonomous mobile robot and utilizes the light-section method. In the apparatus, a particular point is set on an object (to be measured) by projecting a slit light (a light pattern) on the object and by taking an image by a photographing device, and the distance to the point is measured based on the positional relationship between the slit light projecting position and the photographing device.
Specifically, the apparatus is configured such that, the timing of projecting the slit light (that is determined by a duty factor in a pulse train) is varied at random to avoid interference of the sensors mounted on the other mobile robots even in a narrow environmental space where the robots exist. More specifically, pulse rise time (leading edge) in the pulse train whose pulse repetition period T is made constant, is varied at random within a range of the period T, thereby enabling to avoid the interference with the others.
In this kind of sensors, as mentioned in Patent Document Reference 2, the influence of reflection on the object such as caused by an illuminating light unintentionally taken in the image, is reduced by obtaining a difference image between an image taken when the light is projected and an image taken when the light is not projected.                Patent Document Reference 1: Japanese Laid-Open Patent Application No. 2002-156226        Patent Document Reference 2: Japanese Laid-Open Patent Application No. 2001-337166        